Petal colour breaking. Flower of the garden Dahlia (Dahlia sp.) showing the effect of genetics on petal colour. A gene controlling magenta flower colour has been turned on" in part of the flowerhead while it is "switched off" and white in other parts. The flower develops from a small number of cells and depending on when the gene was "turned on" during flower development leads to a smaller or larger part of the plant gaining colour. Shorter duration "on" then "off" gene switching can create streaks or small islands of colour on white petals. Genetic mutations may be induced by 'jumping genes' that move around in the plant's DNA."